1. Field of the Invention
The present invention relates to landing gear structures in aircraft, and more particularly, to systems and methods for determining, e.g., predicting, ground loads applied thereto.
2. Description of the Related Art
Airframe manufacturers typically require that landing gear suppliers provide a detection system to determine if any overload condition occurs. Overload conditions refer to any combination of forces, e.g., stresses, strains and ground loads, which act on the landing gear that cause one or more components to reach design limits and, ultimately, yield. Typically, overload conditions occur during landing, ground maneuvers or towing operations.
Historically detection of overload conditions was limited to pilot opinion and reporting. However, more recent attempts that detect overload conditions use recorded flight data to assess a severity of a landing event which, in turn, is predicts whether an overload condition may have occurred. For example, U.S. Pat. No. 7,589,645 to Schmidt (hereinafter “Schmidt”) discloses an overload detection system that uses accelerometer measurements in combination with flight data from the avionics system to determine if a hard landing occurs. Occurrence of this hard landing can result in an overload condition. However, the approach disclosed in Schmidt proves highly inaccurate since it is predicated on only accelerometer measurements and flight and fails to provide quantitative information of actual loads experienced by the landing gear. In addition, accelerometer measurements and flight data are only available when accelerometers and avionic electronics are operational, e.g., power is on. Accordingly, Schmidt fails to detect if an overload occurs during towing operations whereby aircraft power is off. Further still, Schmidt failure to provide quantitative information of actual loads experienced by the landing gear results in an overwhelming number of erroneously detected overload conditions. Erroneous detection of overload conditions causes an increased cost of maintenance for the landing gear and, ultimately, a delay in future deployment for the aircraft due to required verification inspections that clear the landing gear prior to further flights. The required verification inspections are expensive, time-consuming and complex.
For example, if there are indications of overload conditions after initial visual ground inspections, subsequent inspections on the landing gear are performed during landing gear operation and while the aircraft is placed in suspension, e.g., on aircraft jacks. Thereafter, if these subsequent inspections indicate overload conditions, the entire landing gear is removed and sent to a qualified facility for detailed Non-Destructive Testing (NDT). At present, the entire landing gear is removed, even if only a single landing gear component fails, since, it is not possible to determine individual landing gear component loads and, thus, it is not possible to determine when individual landing gear components reach design limits and fail.
Therefore, there is a need for accurate detection of overload conditions, so as to eliminate unnecessary inspections. Moreover, there is a need for detection of loads upon individual components of the landing gear that are subjected to overload conditions, thereby allowing service technicians to quickly identify only particular component(s) that require further inspection or replacement.
It is also appreciated that, in general, airline industry customers are hesitant to implement new detection systems unless required by the airframe manufacturer and/or aviation authorities. Further, additional detection systems typically correlate to increased costs, such as additional maintenance.
Therefore, there is a need for an inexpensive detection system that objectively and accurately assess the forces experienced by the landing gear and, further, the degree to which particular landing gear components approach design limits caused by the forces, e.g., an overload condition. Such a detection system can confirm or disprove pilot-made hard landing declarations, assure safe aircraft operation and, further, minimize maintenance costs associated therewith.